Wireless communication system advance to provide a seamless communication service to users who are moving around. For doing so, the wireless communication system establishes a cellular network including a plurality of base stations, and each base station provides radio access to terminals in a certain geographical range. The certain geographical range is referred to as a cell, and an area serviced by one cell is referred to as a coverage. In current, a representative example of the wireless communication system for providing a high-speed data communication service includes a Long Term Evolution (LTE) system standardized by 3rd Generation Partnership Project (3GPP), and the LTE system can support high-speed packet based communication which can provide a data rate up to 100 Mbps.
In the wireless communication service over the cellular network, various obstacles can take place according to characteristics of a radio signal. The radio signal, which propagates over an air channel, can be easily blocked by a building or affected by interference. Hence, to address a coverage hole or shadowing problem, a hierarchical cell structure is suggested. According to the hierarchical cell structure, one small cell is deployed in a large cell. Since a distance between a base station and a terminal is relatively short in the small cell, it is easy to attain relatively good channel quality. Thus, the terminal in the small cell can easily access the small cell.
Since the small cell is included in the large cell, a coverage of the small cell is also included in a coverage of the large cell. A method for conducting more efficient communication using dual connectivity by not only accessing the small cell but also maintaining the access to both of the large cell and the small cell is suggested. Hence, the terminal can achieve more efficient communication using more resources.
As discussed above, the terminal can perform the communication using different cells and the multiple connections. In this case, the terminal has two serving base stations. As a result, the terminal has difficulty in determining the base station which controls the communication.